The aggregate net book value of real estate properties serving as collateral for debt as of the balance sheet date.

No definition available.

Name:	gov_AggregateNetBookValueOfRealEstatePropertiesCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The option to extend the maturity date subject to certain conditions and the payment of a fee under the credit facility.

+ References

No definition available.

+ Details

Name:	gov_DebtInstrumentContingentOptionToExtendMaturityDate
Namespace Prefix:	gov_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The anticipated cash outflow during the period from the future repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

Name:	gov_DebtInstrumentNoticeGivenForRepayment
Namespace Prefix:	gov_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the premium percent charged against the amount repaid for unsecured term loan after November 22, 2015 and prior to November 21, 2016.

+ References

No definition available.

+ Details

Name:	gov_LoanPrepaymentPremiumOne
Namespace Prefix:	gov_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the premium percent charged against the amount repaid for unsecured term loan subsequent to November 21, 2016.

+ References

No definition available.

+ Details

Name:	gov_LoanPrepaymentPremiumTwo
Namespace Prefix:	gov_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of mortgage loans on real estate assumed in acquisitions during the period.

+ References

No definition available.

+ Details

Name:	gov_MortgageLoansOnRealEstateAssumedInAcquisitionsNumberOfLoans
Namespace Prefix:	gov_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of buildings serving as collateral for debt as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	gov_NumberOfBuildingsCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of real estate properties serving as collateral for debt as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	gov_NumberOfRealEstatePropertiesCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the calculation of the average interest rate weighted by the amount of long-term debt outstanding by type or by instrument at that time.

+ References

No definition available.

+ Details

Name:	gov_WeightedAverageAnnualInterestRate
Namespace Prefix:	gov_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedPremium
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12317-112629

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12355-112629

+ Details

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

Name:	us-gaap_RepaymentsOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_SeniorNotes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

+ Details

Name:	us-gaap_UnsecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_UnsecuredDebtDueIn2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_UnsecuredDebtDueIn2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_SeniorSecuredNote3.75PercentDueIn2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote5.55PercentDueIn2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote6.21PercentDueIn2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote5.88PercentDueIn2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote7PercentDueIn2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote8.15PercentDueIn2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gov_MortgageNote5.73PercentDueIn2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Indebtedness (Details)		1 Months Ended		12 Months Ended
Indebtedness (Details)	Nov. 21, 2014	Feb. 29, 2016 USD ($) building	Jul. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) property building loan	Dec. 31, 2014 USD ($)	Dec. 31, 2013	Jan. 31, 2016 USD ($) building	Feb. 16, 2015 USD ($)
Indebtedness
Unsecured revolving credit facility				$ 117,000,000
Unsecured term loans				550,000,000	$ 550,000,000
Senior Notes				347,981,000	347,423,000
Mortgage notes payable, net				136,643,000	187,694,000
Total				1,151,624,000	1,085,117,000
Interest rate (as a percent)		6.21%	5.73%				5.55%
Maximum borrowing capacity on revolving credit facility				2,500,000,000
Mortgage note repaid		$ 23,473,000	$ 47,083,000
Debt instrument notice given for repayment							$ 83,000,000
(Gain) loss on early extinguishment of debt				$ (34,000)	$ 1,307,000
Number of properties secured by mortgage notes \| property				5
Number of buildings secured by mortgage notes \| building		1		6			2
Aggregate net book value of secured properties				$ 198,685,000
Number of assumed secured mortgage loans \| loan				5
Unsecured revolving credit facility
Indebtedness
Unsecured revolving credit facility				$ 117,000,000				$ 221,000,000
Interest rate (as a percent)				1.60%
Maximum borrowing capacity on revolving credit facility				$ 750,000,000
Option to extend the maturity date subject to certain conditions and the payment of a fee				1 year
Revolving credit facility, interest rate basis				LIBOR
The weighted average annual interest rate (as a percent)				1.50%	1.70%	1.70%
Interest rate premium (as a percent)				1.25%
Facility fee (as a percent)				0.25%
Unsecured term loan, due in 2020
Indebtedness
Face amount				$ 300,000,000
Unsecured term loans				$ 300,000,000	$ 300,000,000
Interest rate (as a percent)				1.80%
The weighted average annual interest rate (as a percent)	1.90%				1.60%
Term loan, interest rate basis				LIBOR
Interest rate premium (as a percent)				1.40%
Unsecured term loan, due in 2022
Indebtedness
Face amount				$ 250,000,000
Unsecured term loans				$ 250,000,000	$ 250,000,000
Interest rate (as a percent)				2.20%
Term loan, interest rate basis	LIBOR
Interest rate premium (as a percent)				1.80%
Loan prepayment premium prior to November 21, 2016 (as a percent)				1.00%	2.30%
Effective interest rate (as a percent)				2.00%
Loan prepayment premium subsequent to November 21, 2016 (as a percent)				0.00%
3.75% Senior unsecured note due In 2019
Indebtedness
Face amount				$ 350,000
Senior Notes				$ 347,981,000	$ 347,423,000
Interest rate (as a percent)				3.75%
Unamortized fair value discount included in mortgage notes				$ 2,019,000	2,577,000
5.55% Mortgage notes due in 2016
Indebtedness
Mortgage notes payable, net				$ 83,441,000	85,167,000
Interest rate (as a percent)				5.55%
Unamortized fair value premium included in mortgage notes				$ 441,000	2,167,000
6.21% Mortgage notes due in 2016
Indebtedness
Mortgage notes payable, net				$ 23,499,000	23,833,000
Interest rate (as a percent)				6.21%
5.88% Mortgage notes due in 2021
Indebtedness
Mortgage notes payable, net				$ 14,160,000	14,374,000
Interest rate (as a percent)				5.88%
7% Mortgage notes due in 2019
Indebtedness
Mortgage notes payable, net				$ 9,199,000	9,563,000
Interest rate (as a percent)				7.00%
Unamortized fair value premium included in mortgage notes				$ 470,000	605,000
8.15% Mortgage notes due in 2021
Indebtedness
Mortgage notes payable, net				$ 6,344,000	7,339,000
Interest rate (as a percent)				8.15%
Unamortized fair value premium included in mortgage notes				$ 292,000	398,000
5.73% Mortgage notes due in 2015
Indebtedness
Mortgage notes payable, net					47,418,000
Interest rate (as a percent)				5.73%
Unamortized fair value premium included in mortgage notes				$ 0	$ 177,000.000